This work falls within the context of the gênerai pattern of individual monitoring of workers exposed to a risk of internai contamination with actinides. The aim is to propose a new procédure for analyzing Pu traces from urine média and in the présence of uranium. The extradant molécule used is a calix[6]arene bearing hydroxamic acid functions. The affinity of this molécule towards Pu(IV) and U(VI) has been studied and the possibility to separate both éléments has been shown.